Maya Josué, Malloum Alhadji, Fifen Jean Jules, Dhaouadi Zoubeida, Fouda Henri Paul Ekobena, Conradie Jeanet
Department of Physics, Faculty of Science, University of Ngaoundere, Ngaoundere, Cameroon.
National Radiation Protection Agency, Yaounde, Cameroon.
J Comput Chem. 2024 Jun 5;45(15):1279-1288. doi: 10.1002/jcc.27327. Epub 2024 Feb 14.
Through this paper, the authors propose using the quantum cluster equilibrium (QCE) theory to reinvestigate ammonia clusters in the liquid phase. The ammonia clusters from size monomer to hexadecamer were considered to simulate the liquid ammonia in this approach. The clusterset used to model the liquid ammonia is an ensemble of different structures of ammonia clusters. After studious research of the representative configurations of ammonia clusters through the cluster research program ABCluster, the configurations have been optimized at the MN15/6-31++G(d,p) level of theory. These optimizations lead to geometries and frequencies as inputs for the Peacemaker code. The QCE study of this molecular system permits us to get the liquid phase populations in a temperature range of 190-260 K, covering the temperatures from the melting point to the boiling point. The results show that the population of liquid ammonia comprises mainly the ammonia hexadecamer followed by pentadecamer, tetradecamer, and tridecamer. We noted that the small-sized ammonia clusters do not contribute to the population of liquid ammonia. In addition, the thermodynamic properties, such as heat of vaporization, heat capacity, entropy, enthalpy, and free energies, obtained by the QCE theory have been compared to the experiment given some relatively good agreements in the gas phase and show considerable discrepancies in liquid phase except the density. Finally, based on the predicted population, we calculated the infrared spectrum of liquid ammonia at 215 K temperature. It comes out that the calculated infrared spectrum qualitatively agrees with the experiment.
通过本文，作者提出使用量子团簇平衡（QCE）理论重新研究液相中的氨团簇。在这种方法中，考虑了从单体到十六聚体大小的氨团簇来模拟液氨。用于模拟液氨的团簇集是氨团簇不同结构的集合。通过团簇研究程序ABCluster对氨团簇的代表性构型进行深入研究后，在MN15/6-31++G(d,p)理论水平上对构型进行了优化。这些优化得到的几何结构和频率作为Peacemaker代码的输入。对该分子体系的QCE研究使我们能够在190 - 260 K的温度范围内获得液相中的粒子数，涵盖了从熔点到沸点的温度。结果表明，液氨的粒子数主要由氨十六聚体组成，其次是十五聚体、十四聚体和十三聚体。我们注意到小尺寸的氨团簇对液氨的粒子数没有贡献。此外，通过QCE理论获得的热力学性质，如汽化热、热容、熵、焓和自由能，与实验进行了比较，在气相中得到了一些较好的一致性，而在液相中除密度外显示出相当大的差异。最后，基于预测的粒子数，我们计算了215 K温度下液氨的红外光谱。结果表明，计算得到的红外光谱与实验定性一致。
